This invention relates to a fire-retardant polycarbonate composition.
With the increasing demand for the safety of synthetic resins in recent years, higher levels of fire retardancy have been required in providing fire-retardant polycarbonate resins. A number of methods for rendering polycarbonates fire-retardant have been known. Many of them involve the addition of large quantities of organic halogen compounds to polycarbonate resins, as typically shown by the method described in U.S. Pat. No. 3,855,277 which comprises adding poly[2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane carbonate] to a polycarbonate in an amount of as large as 10 to 20% by weight based on the latter. These methods, however, have the defect that toxic gases are generated during combustion, and particularly, the impact strength of the resin is markedly deteriorated.
Addition of inorganic salts has been suggested as one method of remedying this defect. For example, there have been suggested a method of rendering a polycarbonate resin fire-retardant by adding an inorganic sulfite, thiosulfite, dithionite or pyrosulfite to it (see Japanese Laid-Open Patent Publication No. 17558/77), and a method of rendering a polycarbonate resin fire-retardant by adding both such a salt and an organic halogen compound (see Japanese Laid-Open Patent Publication No. 17557/77). However, the use of these inorganic salts causes the defect of markedly degrading the impact strength of the polycarbonate. Furthermore, since these inorganic salts are insoluble in polycarbonate resins, their inclusion impairs the transparency of the polycarbonate resins. Moreover, a sufficient fire retarding effect cannot be obtained unless an organic halogen compound is added.
As other types of improvement, U.S. Pat. No. 4,036,502 discloses a method which involves adding a sulfonic acid metal salt of an aromatic ether, and U.S. Pat. No. 3,978,024 discloses a method which comprises adding a polycarbonate having a metal sulfonate group introduced into the aromatic ring. The fire retarding effects provided by these methods are insufficient, and the thermal stability of the resins is reduced.
The present inventor has now found a novel and excellent fire-retarding agent for polycarbonate resins, and therefore, a fire-retardant polycarbonate composition having superior impact strength and transparency and excellent fire retarding properties which does not generate toxic gases during combustion.